<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>js入门</title>
</head>
<body>
    <!-- js要写在script标签中 -->
    <script>
        // 单行注释
        /*
        多行注释
        */

        // 弹框

        // javascript = ECMAScript + BOM + DOM
        alert('弹框的内容！')
    </script>
</body>
</html>